This invention generally relates to packages for power circuits, and is specifically concerned with a package for a high voltage hybrid circuit having walls formed from an electrically insulative, heat conductive ceramic material, and improved electrical feedthrough structures.
Packages for hermetically sealing power hybrid circuits are known in the prior art. Such packages are typically used in airborne radar systems to protect delicate, heat generating power circuits from thermal overload and mechanical shock. Such packages include a housing formed from a heat conductive metal such as copper or a copper alloy that has been gold plated. The gold-plated base of the housing receives one or more ceramic substrates. Each substrate includes a network of conductive members on its top member, and an array of discrete electronic components and integrated circuits that are soldered onto to various junctions of the conductor network to complete the circuit. The bottom of the substrate is in turn mechanically and thermally connected to the base of the housing by indium-lead solders. A plurality of terminal connectors in the form of terminal posts provide access to the power circuit disposed on the substrates. These posts pass through the walls of the metallic housing, and terminate in thin lead wires which are in turn soldered onto various junctions within the circuit. To prevent the terminal posts from contacting the metallic housing and short-circuiting, each post is mounted in a housing wall by way of a glass post seal. To hermetically seal the circuit from the ambient atmosphere, the housing is filled with an inert gas such as nitrogen, and a metallic cover (which again may be copper or a copper alloy) is sealingly brazed or soldered around the upper edge of the housing.
While such prior art hermetic packages are generally capable of protecting delicate, miniaturized hybrid power circuits from mechanical shock and thermal overload, the applicant has noted a number of areas where the performance of these packages could be improved. For example, the applicant has noted that the glass post seals that insulatively mount the terminal posts through the walls of the housing are difficult to manufacture, and are one of the areas of the package most apt to mechanical failure. Such failure can break the hermetic seal of the package, and may even cause short-circuiting to occur between the various terminal posts and the circuit. The applicant has further observed that, because the maximum diameter of the glass post seals is limited by the height of the walls of the housing, such prior art packages are incapable of handling electrical potential beyond about 2 kilovolts before arcing will occur between the terminal posts and the metal forming the housing walls. Finally, the applicant has noted that the small diameter of the terminal posts used in such prior-art hybrid circuit packages, coupled with the thin lead wires, small bonding areas between these posts and the circuit substrates, and the small spacing between adjacent posts, imposed further limits not only on the maximum voltages that can be conducted through the posts, but on the maximum amperages as well.
Clearly, a hermetic package for a miniaturized hybrid power circuit is needed which offers improved performance over the prior art packages in the areas of maximum voltage and amperage capabilities, and mechanical and electrical reliability. Ideally, such a package would be able to handle large heat loads and thermally induced stresses without mechanical failure, and would be smaller in size, lighter in weight and easier to manufacture than known prior art packages and would not rely upon glass seals to insulatively mount terminals to the walls of the package housing. Finally, it would be desirable if the package could successfully handle large electrical currents without overheating and large voltages without the occurrence of electrical arcing between the terminal posts.